Variable pitch propeller



Feb. 22, 1944. F. E. WILLARD 2,342,442

VARIABLE PITCH PROPELLER Filed Feb. 20, 1941 Patented Feb. 2, 1944' UNITED STATES PATENT orrlca 2,342,442 vmmnu: rl'ron PBOPELLER Franks. Willard, Dallas, Tex. Application February 20, 1941, Serial No. 379,738

3 Claims. (Cl. 170-163) This invention relates to new and useful improvements in variable pitch propellers.

One object of the invention is to provide an improved means for automatically varying the pitch of an airplane propeller while said propeller is revolving or rotating whereby the adjustment of the pitch thereof may be carried out without halting the operation of the propeller, said means being constructed so that the source of power or drive means for the propeller may be utilized to actuate the adjusting means, which eliminates the necessity of providing auxiliary and individual power means for said adjusting means.

An important object of the invention is to provide an improved device which is associated with a propeller having its propeller blades mounted on a hub with each blade being capable of rotation on its longitudinal axis, said device being constructed so that it may be actuated to momentarily retard or resist revolution of the propeller so as to effect a rotation of the blades thereof upon their respective axis and thereby alter the pitch or angular position of said blades.

Another object of the invention is to provide an improved variable pitch device, of the character described, having a portion thereof rotatably confined upon the propeller hub and having connection with the propeller blades so as to be revoluble with said hub and blades and also having a non-rotatable portion adapted to be engaged with the rotatable portion to momentarily retard or resist the revolving of said rotatable portion, whereby the propeller blades will be turned upon their axis so as to decrease the pitch thereof relative to the vertical plane of rotation of the same, said rotatable portion normally tending to prevent axial rotation of the blades so as to aid in maintaining the same in their proper position.

A further object of the invention is to provide an improved variable pitch device which is of a relatively simple and economical construction and which is particularly adaptable to small aircraft or those having low horse-power engines.

The construction designed to carry out the inventions will be hereinafter described together with other features of the invention.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawing, as an example of the invention is shown, and wherein:

Figure 1 is a front elevation of a propeller, constructed in accordance with the invention. mounted on the drive shaft of an airplane,

Figur 2 is an enlarged, transverse, vertical sectional view, taken on the line 2-2 of Fi ure 1, a

Figure 3 is an enlarged, horizontal, cross-sectional view, taken on the line 33 of Figure 1,

Figure 4 is a view, similar to Figure 3, showing one of the propeller blades turned to its decreased pitch position. and

Figure 5 is an isometric view of a portion of the propeller hub, showing the boss formed on the rear surface thereof.

In the drawing, the numerall0 designates the usual housing or casing of an airplane engine (not shown) having a drive shaft ll projecting axially therefrom. The shaft is gradually reduced or tapered inwardly toward its outer forward end to provide an elongate tapered surface I3 and the outer extremity of the shaft is formed with a reduced, screw-threaded pin 12. A cylindrical hub or body I, having an axial bore or opening I! is adapted to be mounted on the shaft II by means of a suitable lock washer l6, and nut l'l which engage upon the screw-threaded outer end of said shaft The bor I5 is centrally disposed within the hub and is complementary to the tapered portion i2 of the shaft so as to receive and snugly engage the same. A counterbore I8 is formed in the extreme outer end of the bore ii for receiving the nut l1 and washer it. As shown in Figure 5, the shaft may be keyed or splined within the bore, whereby rotation of said shaft relative to the other hub is prevented.

A pair of radially extending cylindrical collars I! are preferably formed integral with the hub l4 and are disposed diametrically opposite each other on said hub. Each collar Provides a socket or recess 20, the bottom of which is closed by the wall of the hub H. A pair of propeller blades are adapted to be mounted on the hub and each propeller blade 2| has its inner end enlarged to provide a cylindrical shank 22, which shank is insertable within one of the sockets 20. As illustrated, each shank is of a smaller diameter than its socket and is spaced from the wall thereof, being rotatably supported therein by a pair of ball bearings 23. The latter are preferably spaced from each other and engage within recessed or shouldered portions 24 formed at each end of the shank. The external diameter of the outer race of each bearing 23 is substantially equal to the diameter of its respectiv socket 20 so as to have a snug fit within said socket and maintain the shank in axial alinement therewith. For confining each shank within its socket, a retaining ring 25 is screw-threaded within the outer end of the socket and abuts the external race of the outer bearing 23. Thus, the rings 25 and outer bearings co-act to prevent outward movement or displacement of the blade 2| from the socket. Sincethe shank of each blade is supported within its socket by these bearings, it is obvious that the blades are free- 1:! rotatable upon their respective longitudinal axis relative to the hub it which is, of course, non-rotatable on the shaft i ii.

For limiting the axial rotation of the blades, a plurality of gear teeth 26 are formed on the periphery or exterior of each shank adjacent its inner end just above the inner bearing assembly and these teeth are adapted to mesh with the teeth of a gear rack 2?. The gear racks, which are diametrically-opposed, are preferably made sothat their teeth may mesh-with the gear teeth 26 on the shanks of the propeller blades. The end of the hub beyond the plate 28 is externally screw-threaded at 32 and receives an intemally screw-threaded retaining ring 3;, which engages the outer surface of the plate whereby the plate is rotatably confined upon the hub between the boss and said ring. Obviously, the peripheral flange 30 of the boss encircles the plate and maintains the same in its proper position on the hub.

As is clearly shown in Figure 4, the slots 36 of the boss are of greater length than the gear racks 21 so as to permit a longitudinal movement of said racks-within said slotsupon rotation of the plate 28. This rotationis, of course, limited by the relative lengths of the slots and racks and manifestly since both racks are integral with the teeth a rotation of the plate will cause a simultaneous co-action of both gear racks with their respective blades, whereby both blades will be affected in the same manner, as will be described. Each gear rack is normally held in a predetermined position with relation to the gear teeth, as shown in Figure 3, by means of a coiled or helical spring 34 which is confined between the right end and end wall of each rack and slot with its ends surrounding suitable pins 35 formed thereon. An adjustable set screw 36 projects from the opposite end wall of each slot for engaging the other or adjacent end or the rack, whereby relative movement of the rack in the opposite direction 'may be regulated. It is readily apparent that the adjustment of the set screw and the length of the pins 35 controls the amount or distance of movement of the racks in either direction.

As explained, the springs 36 urge the gear racks Z'l to the position shown in Figure 3 and such movement results in a rotation of the blades M on their respective longitudinal axis through the co-action of the gear racks and gear teeth 28 on said blades. facilitated by their mounting within the bearing assemblies 23 and the amount of rotation is controlled by the adjustment of the set screws 36 which limit the movement of the gear racks. Thus-normally thepitch or angular position of the blades'with respect to the vertical rotation of said blades is as illustrated by the dotted lines in Figure 3, such pitch being relatively increased or high.

The propeller revolves in a counter-clockwise direction in Figure l (to the left in Figure 3), and the parts will remain in this position so long as the plate 28 and gear racks 21 carried there- The rotation of the blades is by are permitted to freely revolve with the hub it and propeller blades. However, if the plate 28 and gear racks are locked or the rotation thereof resisted, then the revolution of the propeller (which is counter-clockwise in Figure 1) will cause the blades 28 thereof to be rotated on their longitudinal axis through the co-action of the gear teet 26 with the gear racks, such rotation of the blades being in a clockwise direction in Figures 3 and 4. Therefore, if the plate 28 is retarded in its rotation to cause the gear racks to become stationary relative to the gear teeth on the blades, the blades will be rotated on their longitudinal axis and such rotation will move said blades to the position shown by dotted lines in Figure 4.. This rotation of the blades imparts movement-of the gear racks against pressure of the springs 36 and the parts will remain in this position so long as rotation of the plate 28 which carries the gear racks is resisted. Obviously. rotation of the blades on their longitudinal axis to the position shown in Figure 4 decreases the pitch of said blades.

For momentarily resisting rotation of the plate 28 and its gear racks 2? on the hub, a U-shaped operating yoke 3'6 is pivotally supported on a bracket 38 which is integral with the engine housing it and which is located adjacent the drive shaft M The yoke 3! is swung on the same are as the plate 28 and is contiguous the rear or outer surface thereof in axial alinement with the same. A brake shoe or friction member 39, of asbestos fabric or other suitable material, is secured to ,each free end of the yoke and is adapted to engage the contiguous surface of the plate upon the swinging or movement of said yoke (Figure 4). For actuating the lever from the cabin or cockpit of the airplane, an operating rod 40 is pivotally connected to an arm which extends outwardly from the intermediate portion of said yoke. Thus, rotation of the plate 28 may be momentarily resisted by swinging the yoke 31' forwardly so as to move the brake shoes 39 into engagement with said plate, whereby the counter-clockwise rotation of the hub it and blades 28 in a vertical plane will force said blades to turn upon their respective axis in a clockwise direction so as to decrease the pitch or angular position of the same (Figure 4). Continued resistance to the rotation of the plate will maintain the blades in their decreased-pitch position due to the engagement of the gear racks of said plate with the gear teeth of said blades. Upon release of the rod 4|], the yoke will swing rearwardly to disengage the shoes 39 from the plate, whereby the coiled springs 36% may exert their force to move the gear racks to their normal position and turn the blades in a counter-clockwise direction (Figure 3). The return of the blades to their increased-pitch po sition will be assisted by the force of the air stream upon said blades, provided the same are of the proper design.

Normally, the blades it are in the position shown in Figures 1 and 3 and revolve in a counter-clockwise direction with the hub i l and shaft 5 l in the usual manner; If the airplane is heavily laden or if there is insufiicient space for said airplane to take off or land safely, it is desirable to increase the R. P. M. or speed of rotation of the propeller blades, whereby the same will produce power in excess of the rated maximum horse-power of the airplane engine. By decreasing the pitch or angular position of the blades relative to the vertical plane of rotation of the propeller, this increase in power may be obtained due to the fact that less air will be displaced upon each revolution of the blades with a consequent; reduction in frictional resistance to the rotation of said blades. Thus the engine will be permitted to operate at an increased or greater speed.

Whenever it is desired to decrease the pitch of the blades 2i so as to produce greater power, the rod 40 is pulled rearwardly so as to swing the yoke 31 forwardly and move the brake shoes 38 into engagement with the plate 28. The frictional engagement of the shoes with the plate will momentarily retard or resist rotation of said plate, whereby the hub I4 and blades 2| will revolve a short distance relative thereto. Since the teeth of the gear racks 21 are constantly meshed with the gear to th 26 of the blades 2|, it is obvious that said b ades will be rotated upon their respective axis relative to the vertical plane of rotation of the propeller. Manifestly, this rotation of the blades will simultaneously move the gear racks and plate to the position shown in Figure 4 due to the engagement between said gear racks and the gear teeth of said blades. These parts will remain in this position so long as the brake shoes 39 are held in frictional engagement with the plate.

After the requirement or necessity for the decreased pitch of the blades has passed, the brake shoes 39 may be disengaged from the plate 28 by releasing the rod 40 so as to permit the lever 31 to swing rearwardly. The force of the springs 34, which have been compressed by the movement of the gear racks relative to the slots 3 I, will then urge said racks in the opposite direction toward the set screws 36, whereby the blades will be rotated upon their respective axis to their normal or high pitch position (Figure 31). It is again noted that excessive or undue movement of the blades, gear racks, and plates is limited by the provision of the set screws 06 and co-acting pins 35. If the blades are of the proper design, the force of the air stream acting upon said blades will aid in returning the same to their high pitch position.

From the foregoing, it is readily apparent that a simple and relatively inexpensive device for varying the pitch of an airplane propeller during revolution thereof has been provided. Although the device is particularly adaptable for use on small or low horse-power airplaneslt can be successfully employed on larger or higher horsepower airplanes. The device contains a minimum number of parts, none of which are complicated, is of sturdy construction and design and is substantially foolproof. Due, to-the simplicity of construction, the device may be readily and quickly installed, removed or replaced by the average airplane mechanic. It is also noted that the principle of operation of the device could also be employed for varying the pitch of multi-bladed propellers without an appreciable change in the construction of the same.

The foregoing description of the invention is explanatory thereof and various changes in the size, shape and materials, as well as in the details of the'iilustrated construction may be made, within the scope of the appended claims, without departing from the spirit of the invention.

What I claim and desire to secure by Letters Patent is:

l. A variable pitch propeller including. a hub. blades mounted on the hub and capable of undergoing rotation about their respective longitudinal axes, gear teeth formed on the periphery of each blade adjacent its inner end, an annular member rotatably confined upon said hub adjacent the blades, gear racks carried by the member and disposed circumferentially of the hub, the gear racks being movable with the member circumferentially of and having their teeth meshed with the gear teeth of said blades, means for resisting rotation of said gear racks and member relative to the hub and blades, whereby said member is the member so as to move the shoes into engagement therewith, whereby rotation of said member may be momentarily resisted so as to turn the blades upon their respective axes and alter the pitch thereof during revolution of the propeller.

2. A variable pitch propeller including, a hub,

r blades mounted on the hub and capable of undergoing rotation about their respective longitudinal axis, gear teeth formed on theperiphery of each blade adjacent its inner end, an annular member rotatably confined upon said hub adjacent the blades, gear racks carried by the member and disposed circumferentially of the hub, the gear racks being movable with the member circumferentially of and having their teeth meshed with the gear teeth of said blades, resilient means for normally holding the gear racks and member in a fixed position relative to the hub and blades, whereby said member is normally rotatable with the hub and blades for preventing rotation of said blades about theirrespective axis, means disposed adjacent the member and adapted to engage the outer surface thereof,'and means for moving the engaging means into engagement with said member, whereby rotation of the member and its gear racks may be momentarily resisted so as to turn the blades upon their respective axis and alter the pitch thereof during revolution of the propeller.

3. A variable pitch propeller including, a hub, blades mounted on the hub and capable of undergoing rotation about their respective longitudinal axis, gear teeth formed on'the periphery of each blade adjacent its inner end, an annular member rotatably confined upon said hub adjacent the blades, gear racks carried by the member and disposed circumferentially of the hub, the gear racks being movable with the member circumferentially of and having their teeth meshed with the gear teeth of said blades, resilient means for normally holding the gear racks and member in a fixed position relative to the hub and blades. whereby said member is normally rotatable with the'hub and blades for preventing rotation of said blades about their respective axis, an element disposed adjacent the member and having means for engaging the outer surface of said member and resisting rotation thereof, and means for moving the element toward the member so as to move the means into engagement therewith, whereby rotation of said member and its gear racks may be momentarily resisted so as to turn the blades upon their respective axis and alter the pitch thereof during revolution of the propeller.

FRANK E. WILLARD. 

